If it's your only carry-on, then I'd highly recommend just bluffing it out.
From their own WizzAir Baggage Policy
As we have limited space onboard, we cannot guarantee that all
passengers’ hand luggage will be travelling with them in the cabin
area of the aircraft.
Only passengers with Wizz Priority will be able to bring their hand
luggage on board subject to boarding procedures at each airport.
These two rules are contradictory. One says it's hit & miss, the other says you have to have paid the extra.
In reality, they always ask for volunteers first if the plane is full.
Just don't volunteer, & if asked specifically tell them it's your camera bag, worth a fortune.
They will just ask someone else instead.
Data source, such as it is:
I never give up my camera bag. I fly with it half a dozen times a year. No-one has ever asked twice after I tell them what's in it - worst case scenario, I took out one of the big lenses, said "three grand" & their expression & demeanour changed immediately.
The bag goes up in the luggage rack with the rest of the carry-on, never in the kick-space.
Just to be clear, it is my only carry-on [unless I'm bringing duty free through on a return trip].
Additionally, it is larger that their 40x30x18 cm rule, but is inside the usual carry-on size of 55x40x23cm.
If you wanted to carry it on as an extra bag, then no doubt you'd have to pay for Priority.
If you purchase the WIZZ Priority service (or you are entitled to WIZZ
Priority with WIZZ Privilege Pass, WIZZ GO or WIZZ Plus bundles) your
hand luggage will be guaranteed to travel with you in the cabin area,
and you will be allowed to carry one additional small bag (a handbag,
a laptop bag or a camera bag) that is not larger than 40 x 30 x 18 cm,
and must be placed under the seat in front of you.